Page 959 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

690 PART 5: Infectious Disorders

a common pathophysiology, diagnostic schemes, and management gram-negative bacilli including Escherichia coli, Klebsiella-Enterobacter
strategies. The classification provided illustrates the classical termi- species, Pseudomonas aeruginosa, and yeast such as Cryptococcus neo-
1,7
nology, which is still frequently used clinically and also facilitates the formans occurs primarily in immunosuppressed or granulocytopenic
understanding of the primary soft tissue planes involved in these soft patients. A severe form of cellulitis may occur in individuals exposed
tissue infections. Depending on the stage of presentation and the rate to Aeromonas hydrophila in fresh water, when the organism gains
of spread, it is important to recognize that an infectious process that access through lacerations during swimming or wading. A severe
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initially may have primarily involved a specific anatomic plane may have and fulminant form of cellulitis that progresses rapidly to necrosis and
progressed to multiple soft tissue planes. bacteremia may be caused by Vibrio species, especially Vibrio vulnificus,
The common superficial pyodermas include erysipelas, impetigo, acquired by exposure of a traumatic wound to salt water or raw seafood
ecthyma, furunculosis, and carbunculosis. These entities do not extend drippings. 7,14
beyond the skin or its appendages and are not discussed further.
The cellulitides include what is commonly referred to as cellulitis, Presentation: Classic cellulitis is characterized by erythema, pain,
anaerobic (or gangrenous) cellulitis, and the clinically distinctive variant edema, and local tenderness involving an area of the skin with ill-
of gangrenous cellulitis called progressive bacterial synergistic gangrene defined borders. The area of initial cutaneous involvement expands
(Meleney gangrene). Cellulitis is an acute spreading infection of the rapidly. There may be associated lymphangitis and regional lymph-
skin extending below the superficial fascia and involving the upper half adenopathy. Systemic manifestations include fever, malaise, and
of the subcutaneous tissues. These infections do not involve the deep rigors. With untreated or rapidly progressive cellulitis, the process
fascial layer. The production of gas by anaerobic organisms and the may spread to involve an entire extremity, producing severe systemic
subsequent presence of soft tissue gas, either palpable or demonstrable toxicity. Dehydration, mental apathy or obtundation, disseminated
radiographically, and the propensity to produce necrosis in the sub- intravascular coagulopathy, respiratory failure, and septic shock may
cutaneous tissue (and eventually in the skin) are major differentiating follow, necessitating intensive care management.
features of anaerobic and classic cellulitis. Both of these latter entities Management: Appropriate laboratory diagnostic studies should be
may progress to suppuration and lead to a subcutaneous and/or cutane- performed before antimicrobial therapy is begun. Any skin abrasions
ous abscess. Progressive bacterial synergistic gangrene (Meleney gangrene) or draining sites should be swabbed for immediate Gram stain and
was the original term used to describe a distinct form of cellulitis often culture. The stain is examined for the presence of organisms, their
occurring postoperatively, with necrotic ulcer formation in the center of morphologic appearance, and the number and types of cells. Fine nee-
a cellulitic area. 9 dle aspiration into the leading edge of the cellulitis may be attempted;
Necrotizing fasciitis is an acute infection involving the deep fascia, potential pathogens have been isolated in 10% to 38% of cases. 15,16
subcutaneous tissue, and superficial fascia to variable degrees. The A combination of needle aspiration, skin biopsy, and blood cultures
10
muscle tissue beneath the deep fascia is unaffected. The skin may not results in isolation of pathogens in approximately 25% of cases. 17
be involved early in the course of the infection, but as the process con- For severe infections in which streptococci and methicillin-susceptible
tinues the skin becomes involved. Fournier syndrome (or gangrene) is staphylococci are considered possible, parenteral administration of a
a form of necrotizing fasciitis that affects the scrotum and genitalia. large-dose penicillinase-resistant penicillin (nafcillin or cloxacillin),
11
In this setting, because there is virtually no subcutaneous fat between 8 to 12 g/day in four or six divided doses, is most appropriate. Alternate
the epidermis and dartos fascia, cutaneous gangrene readily develops. agents include a first-generation cephalosporin, such as cefazolin
The myonecroses include clostridial myonecrosis (otherwise known (6 g/day in three divided doses), vancomycin (2 g/day in two divided
as gas gangrene), nonclostridial myonecrosis (which has also been doses), or clindamycin (1200-2400 mg/day in three divided doses). In
termed synergistic necrotizing cellulitis, although that is a misnomer), settings where community- or hospital-associated MRSA predominate,
pyomyositis, and vascular gangrene. Rapid necrosis of the muscle and which is increasingly encountered in many jurisdictions, vancomycin
subsequent necrosis of the overlying subcutaneous tissue and skin are (2 g/day in two divided doses) or another agent with reliable activity
characteristic of the myonecrotic syndromes. Pyomyositis, an exception, against MRSA in skin and soft tissue infections, including linezolid,
is a bacterial abscess localized to the muscle, usually occurring after daptomycin, or ceftaroline is indicated. An additional approach rec-
7,18
penetrating trauma. Vascular gangrene occurs in a limb devitalized by ommended by some authors is to use a penicillinase-resistant penicillin
arterial insufficiency. (nafcillin or cloxacillin) or a first-generation cephalosporin in addition
to vancomycin. If the etiologic agent proves to be streptococcal,
19
MAJOR SOFT TISSUE INFECTIONS penicillin G should be substituted (6-12 million U/day). In the immu-
■ CELLULITIS nocompromised host, empiric broad-spectrum administration of agents
active against both gram-positive, including MRSA, and gram-negative
Pathogenesis: Cellulitis most often occurs secondary to trauma of organisms is appropriate such as a combination of vancomycin plus an
the skin with local inoculation of microorganisms, secondary to an antipseudomonal cephalosporin or a carbapenem or an aminoglyco-
18
underlying skin lesion or a postoperative wound infection, or by side plus an extended spectrum penicillin agent. In the presence of a
contiguous spread from a suppurative infection of other soft tissues rapidly progressive cellulitis developing after a freshwater or saltwater
or bone. However, cellulitis may also occur in the absence of any exposure, where Aeromonas or Vibrio, respectively, may be potential
obvious local trauma. After inoculation of microorganisms into the pathogens, alternative agents are more appropriate . Aminoglycosides,
subcutaneous tissues and skin, an acute inflammatory response is third-generation cephalosporins, and carbapenems have reliable activ-
seen in the epidermis, dermis, adipose tissue, and superficial fascia, ity versus Aeromonas hydrophila and any of these agents represents an
to varying degrees. appropriate empiric choice. A combination of a third-generation cepha-
losporin (cefotaxime or ceftazidime) with doxycycline has synergistic
Etiology: The most common organisms causing classic cellulitis are activity against Vibrio vulnificus and some reports have suggested an
Streptococcus pyogenes and S aureus, with other streptococci (groups improved outcome with this combination for the treatment of Vibrio
B, C, F, and G), Streptococcus pneumoniae, and gram-negative bacilli vulnificus infections. 20
encountered less frequently. Over the past decade, community-associated Local care of cellulitis includes immobilization and elevation of the
methicillin-resistant S aureus (CA-MRSA), predominantly of the USA affected area. These measures are most appropriate when an extremity
300 pulsotype and containing the Panton-Valentine leukocidin, has been is affected. Analgesic drugs are administered as necessary. Cool com-
increasingly associated with a progressive type of cellulitis, often sup- presses may help alleviate pain. The extent of the cellulitis should be
purating and causing large subcutaneous abscesses. Cellulitis due to outlined on the skin with an appropriate marker at the time of admission
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